The present invention relates to an apparatus and a method for the replacement of posterior vertebral elements, and more particularly to an apparatus and a method that replaces posterior vertebral elements while preserving spinal stability and mobility.
The human spine 29 comprises individual vertebrae 30 that interlock with each other to form a spinal column, shown in FIG. 1A. Referring to FIGS. 1B, 1C, and 1D, each vertebra 30 has a cylindrical bony body (vertebral body) 32, two pedicles 48 extending from the vertebral body 32, a lamina 47 extending from the pedicles 48, three winglike projections (two transverse processes 33, 35 extending from the pedicles 48 and one spinous process 34 extending from the lamina 47), pars interarticularis 36, two superior facets 46 extending from the pedicles 48 and two inferior facets 45 extending from the lamina 47. The pars interarticularis 36 connects the superior 46 and inferior 45 facets on either side of the spinous process 34. The bodies of the vertebrae 32 are stacked one on top of the other and form the strong but flexible spinal column. The spinous process 34, lamina 47, pars interarticularis 36, superior facets 46, inferior facets 45, transverse processes 33, and pedicles 48 are positioned so that the space they enclose forms a tube, i.e., the spinal canal 37. The spinal canal 37 houses and protects the spinal cord and other neural elements. A fluid filled protective membrane, the dura 38, covers the contents of the spinal canal. The spinal column is flexible enough to allow the body to twist and bend, but sturdy enough to support and protect the spinal cord and the other neural elements.
The vertebrae 30 are separated and cushioned by thin pads of tough, resilient fiber known as inter-vertebral discs 40. Inter-vertebral discs 40 provide flexibility to the spine and act as shock absorbers during activity. There is a small opening (foramen) 42 between each vertebra 30, through which nerves 44 pass and go to different body parts. When the vertebrae are properly aligned the nerves 44 pass through without a problem. However, when the vertebrae are misaligned or a constriction 45 is formed in the spinal canal, the nerves get compressed 44a and may cause back pain, leg pain or other neurological disorders. Disorders of the spine that may cause misalignment of the vertebrae or constriction of the spinal canal include spinal injuries, infections, tumor formation, herniation of the inter-vertebral discs (i.e., slippage or protrusion), arthritic disorders, and scoliosis. In these pathologic circumstances, surgery may be tried to either decompress the neural elements and/or fuse adjacent vertebral segments. Decompression may involve laminectomy, discectomy, or corpectomy. Laminectomy involves the removal of part of the lamina 47, i.e., the bony roof of the spinal canal. Discectomy involves removal of the inter-vertebral discs 40. Corpectomy involves removal of the vertebral body 32 as well as the adjacent disc spaces 40. Laminectomy and corpectomy result in central exposure of the dura 38 and its contents. An exposed dura 38 puts the neural elements and spinal cord at risk from direct mechanical injury or scarring from overlying soft tissues. Scarring is considered a major cause for failed back syndrome in which patients continue to have back and leg pain after spinal surgery. Current methods to decrease the risk of developing this syndrome include covering the dura with fat harvested from the patient""s subcutaneous tissues or using a synthetic material. However, no material as yet has been used that completely or significantly prevents scarring of the dura and nerve roots after spine surgery in humans.
Furthermore, laminectomy predisposes the patient to instability through the facet joints and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction. Therefore the surgeon needs to stabilize the spine after laminectomy procedures and after corpectomy. One spine stabilization method is fusion. Fusion involves the fixation of two or more vertebrae. Fusion works well because it stops pain due to movement of the intervertebral discs 40 or facets 45, 46, immobilizes the spine, and prevents instability and or deformity of the spine after laminectomy or corpectomy. However, spinal fusion limits spinal mobility. Maintaining spinal mobility may be preferred over fusion in some cases to allow more flexibility of the spine and to decrease the risk of junction problems above and below the level of the fixation due to increased stress.
An arthritic facet joint may also cause back pain. Since the majority of the motion along the spine occurs at the facet joints, fusing the diseased facet would often relieve pain but again at a high cost of fusing across at least one spinal segment thus preventing motion and effectively increasing stresses at the adjacent facet joints. Increased stresses predispose facet joints to accelerated arthritis, pain, and instability requiring additional surgery to fuse these levels. This cyclic process results in an overall decreased mobility of the spine. Therefore, it is an attractive alternative to attempt to replace the diseased facet without resorting to fusion, thus avoiding significant limitation in mobility of the spine. The obvious solution would be to replace the opposing surfaces of each facet to preserve motion between the surfaces. Any efforts to replace the facets at their natural location necessitate destroying the facet capsule and risks producing an unstable joint. It would be desirable to achieve spine stabilization that preserves mobility, protects the contents of the spinal canal, does not cause tissue scarring, decreases pain in the facet joints, and does not always destroy the facet capsule.
In general, in one aspect, the invention features an orthopedic implantable device articulately connecting a first spinal vertebra to an adjacent second spinal vertebra. Each spinal vertebra includes a vertebral body, a pair of pedicles extending posteriorly from the vertebral body, a lamina extending from the pedicles, a pair of superior facets extending from the pedicles, a pair of inferior facets extending from the lamina, a pair of pars interarticularis connecting the superior and inferior facets, a spinous process extending from the lamina and a pair of transverse processes extending from the pedicles. The orthopedic implantable device includes a first component adapted to be attached to a posterior location of the first vertebra and a second component adapted to be attached to a posterior location of the second vertebra. The first component is articulately connected to the second component.
Implementations of this aspect of the invention may include one or more of the following features. The first component may be articulately connected to the second component along a posterior midline of the first and second vertebrae and/or along an axis medial to the facets of the vertebrae. The first component may comprise a body and at least one male articulation member attached to the first component body and the second component may comprise a body and at least one female articulation member attached to the second component body and the first component may be articulately connected to the second component by engaging the at least one male articulation member to the at least one female articulation member. The at least one male articulation member may comprise a hook and the at least one female articulation member may comprise a loop. The first component body may further comprise at least one female articulation member and the second component body may further comprise at least one male articulation member. The posterior locations of the first and second vertebrae are selected from a group including a pedicle, transverse processes, facets, lamina, pars interarticularis, and vertebral body. The body of the first component may be attached to first and second pedicles of the first vertebra and the body of the second component may be attached to first and second pedicles of the second vertebra, respectively. The first and second components may be attached to the first and second vertebrae, respectively, via screws, wires, or hooks. The first component may be articulately connected to the second component via a hinge. The first and second components may have adjustable width and the width may be adjusted between 20 and 80 millimeters.
In general, in another aspect, the invention features an orthopedic implantable device articulately connecting a plurality of individual vertebrae. The vertebrae are adjacent to each other and form a segment of a spinal column. The orthopedic device includes a plurality of individual components, and each component is adapted to be attached to a posterior location of an individual vertebra. Each of the individual components is articulately connected to an adjacent inferior and an adjacent superior component along a posterior midline of the spinal column or any axis medial to the facets.
Implementations of this aspect of the invention may include one or more of the following features. Each component may comprise a body, at least one female articulation member formed within the body, and at least one male articulation member attached to the body. Each of the individual components may be articulately connected to an adjacent inferior component by engaging the at least one male articulation member to the at least one female articulation member of the adjacent inferior component, and each of the individual components may be articulately connected to an adjacent superior component by engaging the at least one female articulation member to the at least one male articulation member of the superior component.
In general, in another aspect, the invention features an orthopedic implantable component adapted to replace a posterior element of a vertebra. The vertebra comprises a vertebral body, a pair of pedicles extending posteriorly from the vertebral body, a lamina extending from the pedicles, a pair of superior facets extending from the pedicles, a pair of inferior facets extending from the lamina, a pair of pars interarticularis connecting the superior and inferior facets, a spinous process extending from the lamina and a pair of transverse processes extending from the pedicles. The orthopedic component includes a body adapted to be attached to a posterior location of the vertebra, a male articulation member extending from the body, and a female articulation member formed within the body.
Implementations of this aspect of the invention may include one or more of the following features. The body may be configured to replace the lamina, the spinous process, pars interarticularis, and the superior and inferior facets of the vertebra. The body may be attached to the pedicles of the vertebra via screws threaded through apertures formed in the body. The screws may be made of stainless steel, titanium, gold, silver, alloys thereof, plastic, absorbable or biodegradable material. The orthopedic implantable component may be made of metal, plastic, ceramic, bone, polymers, composites, absorbable material, biodegradable material, and combinations thereof. The male articulation member may be a hook and the female articulation member may be a bar connecting opposite sides of a cavity formed within a bottom surface of the body. The cavity may be arranged along a midline of the body or along any axis medial to the facets.
In general, in another aspect, the invention features a spine stabilization method articulately connecting a first vertebra to a second vertebra including the following steps. First providing a first component and attaching the first component to a posterior location of the first vertebra. Next, providing a second component and attaching the second component to a posterior location of the second vertebra. Finally, articulately connecting the first component to the second component.
In general, in another aspect, the invention features a spine stabilization method connecting a first vertebra to a second vertebra including the following steps. First attaching first and second screws to first and second locations, respectively, of the first vertebra. Next attaching third and fourth screws to first and second locations, respectively, of the second vertebra. Next providing first and second components, the first and second components comprising a body and being articulately connected to each other along a midline of the bodies. Next attaching the body of the first component to the first and second locations of the first vertebra via the first and second screws, respectively. Next, attaching the body of the second component to the first and second locations of the second vertebra via the third and fourth screws, respectively. Finally, tightening of all said screws.
Implementations of this aspect of the invention may include before attaching the bodies of the first and second components adjusting the width of the bodies of the first and second components.
Among the advantages of this invention may be one or more of the following. The implantable spinal stabilization device stabilizes the spine, while allowing the patient to retain spinal flexibility by preserving motion between adjacent vertebras. The spinal stabilization device may be used for the treatment of a multitude of spinal disorders including facet arthritis and spinal stenosis. The device covers and protects the posterior central neural elements after laminectomy, and replaces diseased or injured facet joints without fusing across vertebral segments. The invention can be used to replace the spinous process, laminas, and facets individually or in combination at each vertebra. The implantable device has a compact structure and low profile. By virtue of transferring the motion between adjacent vertebras from the diseased or iatrogenically injured facets laterally towards the midline, the spine is stabilized but also allows motion between the vertebrae. This is a desirable feature when compared to fusion in selected cases where preserving a patient""s spinal mobility is preferred.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims.